428 GLOSSARY 



Trichi'na: pork worm, a parasitic roundworm causing the condition called 



trichinosis. 

 Tro'pism (Gr. tropein, to turn) : a definite response of an organism to one of 



the forces in its environment. 

 Tryp'anosomes (Gr. trypanon, an auger) : protozoa which cause disease such 



as sleeping sickness. 

 Tym'panum (Gr. tympanon, a drum) : the eardrum. 



U 



U'rea (Lat. urina, urine) : a nitrogenous waste excreted in the urine. 



Vaccina'tion : inoculation with a vaccine, containing living or dead micro- 

 organisms or their toxins, in order to protect the body from disease. 



Vac'cine : a substance made from living or dead organisms, which, when inoc- 

 ulated into the body, protects against a specific disease. 



Vac'uole (Lat. vacuus, empty) : a space in protoplasm containing air, water, 

 sap, or food material. 



Varia'tion: in biology, the occurrence of differences between individuals of 

 the same species. 



Vein : a tube which conveys blood to the heart. 



Ve'nae ca'vae : vessels through which the blood returns to the right auricle 

 of the heart. 



Ventila'tion (Lat. ventilare, to air) : changing of air in a room or building. 



Ven'tral (Lat. venter, belly) : the opposite of dorsal. 



Ven'tricle (Lat. ventriculus, a little belly) : a muscular chamber of the heart, 

 which forces the blood out. 



Ver'mifonn appendix (Lat. vermis, worm) : a narrow tube about four inches long, 

 closed at the outer end, near the beginning of the large intestine of man. 



Ver'tebrae (Lat. verier e, to turn) : bones of the vertebral column. 



Ver'tebrate : an animal having a backbone. 



Villus (Lat. villus, shaggy hair) : a minute projection, an absorbing organ 

 of the small intestine. 



Vi'tamin (Lat. vita, life) : unknown substances in food apparently necessary 

 to support life. 



Voruntary (Lat. voluntas, will) : subject to the will (used with reference to 

 muscles), as opposed to involuntary. 



X 



Xy'lem (Gr. xylon, wood) : the inner woody part of a fibrovascular bundle 

 which conducts water up the stem, 



Z 



Zy'gospores or Zy'gotes : spores formed by union of sex cells. 



